Method for controlling specific resistance of single crystal and an apparatus therefor

Abstract

A method for controlling a specific resistance of a single crystal in a Czochralski-method type single crystal pulling apparatus having a hermetical chamber in which the single crystal is pulled up from a polycrystal melt and an inert gas supply and exhaust system by means of which an inert gas is supplied to the hermetical chamber and exhausted therefrom; the method being characterized in that the pneumatic pressure in the hermetical chamber and the supply rate of the inert gas are controlled in accordance with a prepared control pattern with respect to the passage of pulling time.

What is claimed is: 
     
       1. A method for controlling a specific resistance of a single crystal which is grown in a Czochralski-method type single crystal pulling apparatus having a hermetical chamber in which the single crystal is pulled up from a polycrystal melt and an inert gas supply and exhaust system by means of which an inert gas is supplied to said hermetical chamber and exhausted therefrom; said method being characterized in that the pneumatic pressure in said hermetical chamber and the supply rate of said inert gas are controlled in accordance with a prepared control pattern with respect to the passage of pulling time, wherein said prepared control pattern is obtained by first solving the following partial differential equation for (∂P/∂t) F  and (∂F/∂t) P  such that K Sb  =1:   K.sub.Sb =aP.sub.0 +b(∂P/∂t).sub.F +cF.sub.0 +d(∂F/∂t).sub.P +e     wherein a, b, c, d, and e are empirically obtained coefficients, P is the pressure in said chamber, F the inert gas flow rate, t the time passage of the pulling operation, K Sb  the segregation coefficient of a Sb dopant in the silicon melt, P 0  the initial value of said chamber pressure P, F 0  the initial value of said inert gas flow rate F; then, programming the values of the pneumatic pressure P in said chamber and the inert gas flow rate F with respect to the time passage t of the pulling operation.   
     
     
       2. The method as claimed in claim 1, wherein said prepared control pattern is such that the pneumatic pressure in said hermetical chamber is varied while the supply rate of said inert gas is kept unchanged. 
     
     
       3. The method as claimed in claim 1, wherein said prepared control pattern is such that the supply rate of said inert gas is varied while the pneumatic pressure in said hermetical chamber is kept unchanged. 
     
     
       4. A method for controlling a specific resistance of a single crystal which is grown in a Czochralski-method type single crystal pulling apparatus having a hermetical chamber in which the single crystal is pulled up from a polycrystal melt and an inert gas supply and exhaust system by means of which an inert gas is supplied to said hermetical chamber and exhausted therefrom; said method being characterized in that the pneumatic pressure in said hermetical chamber and the supply rate of said inert gas are controlled ion accordance with a prepared control pattern with respect to the passage of pulling time, wherein said prepared control pattern is obtained by first solving the following partial differential equation for (∂P/∂t) F  such that K Sb  ≈1:   K.sub.Sb =aP.sub.0 +b(∂P/∂t).sub.F +CF.sub.0 +e     wherein a, c, and e are empirically obtained coefficients, P is the pressure in said chamber, F the inert gas flow rate, t the time passage of the pulling operation, K Sb  the segregation coefficient of a Sb dopant in the silicon melt, P 0  the initial value of said chamber pressure P, F 0  the initial value of said inert gas flow rate F; then, programming the value of the pneumatic pressure P in said chamber with respect to the time passage t of the pulling operation.   
     
     
       5. A method for controlling a specific resistance of a single crystal which is grown in a Czochralski-method type single crystal pulling apparatus having a hermetical chamber in which the single crystal is pulled up from a polycrystal melt and an inert gas supply and exhaust system by means of which an inert gas is supplied to said hermetical chamber and exhausted therefrom; said method being characterized in that the pneumatic pressure in said hermetical chamber and the supply rate of said inert gas are controlled ion accordance with a prepared control pattern with respect to the passage of pulling time, wherein said prepared control pattern is obtained by first solving the following partial differential equation for (∂F/∂t) P  such that K Sb  ≈1:   K.sub.Sb =aP.sub.0 +cF.sub.0 +d(∂F/∂t).sub.P +e     wherein a, b, c, d, and e are empirically obtained coefficients, P is the pressure in said chamber, F the inert gas flow rate, t the time passage of the pulling operation, K Sb  the segregation coefficient of a Sb dopant in the silicon melt, P 0  the initial value of said chamber pressure P, F 0  the initial value of said inert gas flow rate F; then, programming the value of the inert gas flow rate F with respect to the time passage t of the pulling operation.   
     
     
       6. An apparatus for controlling the specific resistance of a single crystal which is grown in a Czochralski-method type single crystal pulling apparatus having: a hermetical chamber in which a single crystal is pulled up from a polycrystal melt;   an inert gas system including an inert gas supply source, an inert gas supply passage via which said inert gas supply source communicates with said chamber, an inert gas exhaust passage, and a vacuum pump by means of which an inert gas is supplied to said hermetical chamber and exhausted therefrom; said apparatus being characterized by comprising:   a flow rate control means provided across said inert gas supply passage for controlling the supply rate of said inert gas to said hermetical chamber;   a control valve means provided across said exhaust passage via which said chamber communicates with said vacuum pump, for controlling the pressure in said hermetical chamber;   a pressure sensor for detecting the pressure in said hermetical chamber;   a central processing unit for controlling said control valve means and said flow rate control means responsive to the pressure detected by said pressure sensor in a manner such that the pressure in the chamber and the inert gas flow rate are controlled in accordance with a prepared control pattern with the respect to the passage of pulling time, including   means for determining said pressure and said inert gas flow rate during pulling time of said single crystal ingot from a melt by solving the following partial differential equation for (∂P/∂ t) F  and (∂F/∂ t) P  such that K Sb  ≈1:   K.sub.Sb =aP.sub.o +b(∂P/∂t).sub.P +cF.sub.o +d(∂F/∂t).sub.p +e     where a, b, c, d, e are empirically obtained coefficients, P is the pressure in said chamber, F the inert gas flow rate, t is the time passage of the pulling operation, K Sb  the segregation coefficient of a Sb dopant in the silicon melt, P o  the initial value of said chamber pressure P, and F o  the initial value of said inert gas flow rate F.     
     
     
       7. The apparatus as claimed in claim 6 wherein said control valve means is a conductance valve. 
     
     
       8. The apparatus as claimed in claim 7 wherein said conductance valve includes an electrically operated needle valve. 
     
     
       9. An apparatus for controlling the specific resistance of a single crystal which is grown in a Czocharalski-method type single crystal pulling apparatus having: a hermetical chamber in which a single crystal is pulled up from a polycrystal melt;   an inert gas system including an inert gas supply source, an inert gas supply passage via which said inert gas supply source communicates with said chamber, an inert gas exhaust passage, and a vacuum pump by means of which an inert gas is supplied to said hermetical chamber and exhausted therefrom; said apparatus being characterized by comprising:   a flow rate control means provided across said inert gas supply passage for controlling the supply rate of said inert gas to said hermetical chamber;   a control valve means provided across said exhaust passage via which said chamber communicates with said vacuum pump, for controlling the pressure in said hermetical chamber;   a pressure sensor for detecting the pressure in said hermetical chamber;   a central processing unit for controlling said control valve means and said flow rate control means responsive to the pressure detected by said pressure sensor in a manner such that the pressure in the chamber and the inert gas flow rate are controlled in accordance with a prepared control pattern with the respect to the passage of pulling time, including   means for determining said pressure and said inert gas flow rate during pulling time of said single crystal ingot from a melt by solving the following partial differential equation for (∂P/∂t) F  such that K Sb  ≈1:   K.sub.Sb =aP.sub.o +b(∂P/∂t).sub.F +cF.sub.o +e     wherein a, b, c, e are empirically obtained coefficients, P is the pressure in said chamber, F the inert gas flow rate, t the time passage of the pulling operation, K Sb  the segregation coefficient of a Sb dopant in the silicon melt, P O  the initial value of said chamber pressure P, F O  the initial value of said inert gas flow rate F.     
     
     
       10. An apparatus as recited in claim 9, wherein said control valve means is a conductance valve. 
     
     
       11. An apparatus as recited in claim 10, wherein said conductance valve is a needle valve. 
     
     
       12. An apparatus for controlling the specific resistance of a single crystal which is grown in a Czochralski-method type single crystal pulling apparatus having: a hermetical chamber in which a single crystal is pulled up from a polycrystal melt;   an inert gas system including an inert gas supply source, an inert gas supply passage via which said inert gas supply source communicates with said chamber, an inert gas exhaust passage, and a vacuum pump by means of which an inert gas is supplied to said hermetical chamber and exhausted therefrom; said apparatus being characterized by comprising:   a flow rate control means provided across said inert gas supply passage for controlling the supply rate of said inert gas to said hermetical chamber;   a control valve means provided across said exhaust passage via which said chamber communicates with said vacuum pump, for controlling the pressure in said hermetical chamber;   a pressure sensor for detecting the pressure in said hermetical chamber;   a central processing unit for controlling said control valve means and said flow rate control means responsive to the pressure detected by said pressure sensor in a manner such that the pressure in the chamber and the inert gas flow rate are controlled in accordance with a prepared control pattern with respect to the passage of pulling time, including   means for determining said pressure and said inert gas flow rate during pulling time of said single crystal ingot from a melt by solving the following partial differential equation for (∂F/∂t) P  such that K Sb  ≈1:   K.sub.Sb =aP.sub.O +cF.sub.O +d(∂F/∂t).sub.P +e.     wherein a, c, d, e are empirically obtained coefficients, P is the pressure in said chamber, F the inert gas flow rate, t the time passage of the pulling operation, K Sb  the segregation coefficient of a Sb dopant in the silicon melt, P O  the initial value of said inert gas flow rate F; then, programming the value of the insert gas flow rate F with respect to the time passage t of the pulling operation.     
     
     
       13. An apparatus as recited in claim 12, wherein said control valve means is a conductance valve. 
     
     
       14. An apparatus as recited in claim 13, wherein said conductance valve is a needle valve. 
     
     
       15. The method as claimed in claim 4, wherein said prepared control pattern is such that the pneumatic pressure in said hermetical chamber is varied while said supply rate of said inert gas is kept unchanged. 
     
     
       16. The method as claimed in claim 4, wherein said prepared control pattern is such that the supply rate of said inert gas is varied while said pneumatic pressure in said hermetical chamber is kept unchanged. 
     
     
       17. The method as claimed in claim 5, wherein said prepared control pattern is such that the pneumatic pressure in said hermetical chamber is varied while said supply rate of said inert gas is kept unchanged. 
     
     
       18. The method as claimed in claim 5, wherein said prepared control pattern is such that the supply rate of said inert gas is varied while said pneumatic pressure in said hermetical chamber is kept unchanged.